Individual Sperm Genomes Sequenced for First Time

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For the first time, researchers have sequenced the entire genome
of the human sperm cell.

The findings, reported today (July 19) in the journal Cell, may
help researchers understand the genetic mixing that ensures that
babies end up with an even blend of DNA.

A new understanding of the sperm genome may have "far-ranging
implications for the study of cancer,
infertility and many other disorders," study researcher
Stephen Quake, a bioengineer at Stanford University, said in a
statement.

Quake and his colleagues sequenced the genomes of 91 sperm cells
from a 40-year-old man with a healthy semen sample and normal
children. They found a surprising level of variability between
the cells. For example, two of the sperm cells were missing
entire chromosomes.

Gametes -- egg cells and sperm cells -- hold half of the
amount DNA found other cells of an organism. A human cell has 23
pairs of matched chromosomes, or bundles of DNA; sperm and egg
cells have 23 single chromosomes.

To ensure an even blend of genes from both sets of parents (and,
in turn, from all four grandparents), gametes go through a
process called recombination. During recombination, DNA strands
can break apart and join new strands, creating new mixes of
genes.

Until now, researchers have been limited to studying the genes of
large groups of people to estimate how much recombination occurs
in gametes. But in the new study, the researchers were able to
compare the man's sperm
cells to his body cells, with their full compliment of DNA.

They found that recombination occured 23 times, on average, in
the sperm cells. Some cells had more recombined genes more than
others, however, and the rate of
genetic mutations between cells varied widely, the
researchers reported. They identified between 25 and 36
single-nucleotide mutations in each sperm cell. Some of these
mutations could be beneficial, others could be harmful or even
deadly to an embryo.

"Now, we can look at a particular individual, make some calls
about what they would likely contribute genetically to an embryo
and perhaps even diagnose or detect potential problems," study
co-author Berry Behr, a professor of obstetrics and gynecology at
Stanford, said in a statement.